Titan is a rocky moon, with a dense atmosphere and a gravity well somewhat weaker than Earth's. There are methane seas, and methane makes up a significant portion of the atmosphere (the majority being nitrogen). It is relatively cold, due to its distance from Sola.
Titan captured human attention when it was discovered that not only did Titan sustain an atmosphere, but that it had water. Early attempts to colonize the moon were unsuccessful. But when the Federation took control of the project, a permanent human settlement was established.
Louis Spectra lived on Titan for his earlier Starfleet career.
Federation Colonization Committee
During the early 23rd century, the Federation set out to terra-form and colonize such worlds which could be colonized without violating the Prime Directive. To this end, the Federation Colonization Committee was established. This provided for many of the fundamental needs for terra-forming a planet or establishing a colony.
In regards to Titan, the FCC paid little heed to Titan, since it was a moon of a planet of the Terran Solar System. Therefore, no measures were taken to terra-forming it for the creation of a permanent colony. Instead, atmospheric shields were set up around the site of colonization. Atmospheric generators would create a breathable M-class atmosphere within the shield bubble without damaging Titan.
Lunar Colony 7
Titan was the 7th Inter-System moon to be colonized by the FCC. The colony was established on the shores of one of the largest methane lakes on the planet: this lake was called Lake Titan.
Norse Mythological Anomaly
One of Saturn's moons, named after the mythic wolf Fenrir, has a perigee once every one hundred years to Titan. There is an island in the middle of Lake Titan that has been nicknamed "Odin's Isle". During the perigee, when the moon Fenrir is at its zenith over Odin's Isle, an odd calcium deposit glows in the light of the moon. This is odd for two reasons: 1) calcium is extremely rare on Titan and 2) the shape of the deposit resembles a man with a spear on an eight-legged horse being devoured by a wolf.